1. Field of the Invention
The present invention relates to an imaging apparatus and method, and its control method and, more particularly, to an imaging apparatus such as a digital camera which saves a photographed image as an electrical signal in the apparatus, and an imaging method.
2. Description of the Related Art
Along with developments of imaging processing techniques in recent years, imaging apparatuses such as digital still cameras that use these techniques have been developed remarkably. FIG. 18 shows the arrangement of a digital still camera, and its operation will be briefly described below.
Referring to FIG. 18, reference numeral 91 denotes a camera operation unit, which includes a main switch, release switch, and the like of a camera. The camera operation unit 91 is operated by the user, and an overall controller 80 detects a change in state of the main switch, and starts power supply to other building blocks.
An object image within the photographing range is formed on an imaging unit 82 via a main photographing optical system 81, and an electrical signal output from the imaging unit 82 is converted into a predetermined digital signal via an A/D (Analog to Digital) converter 83 in turn in units of pixels. The converted digital signal is input to a process controller 84. The process controller 84 generates R, G, and B color signals on the basis of the pixel data sent from the imaging unit 82. Before normal photographing, these color signals are transferred to a video memory 89 via a memory controller 85 periodically, e.g., in units of frames, thus making a finder display or the like using a monitor display 90.
When the user photographs by operating the camera operation unit 91, image data for one frame sent from the process controller 84 is stored in a frame memory 86 in response to a control signal from the overall controller 80, and the data in the frame memory 86 is compressed by the memory controller 85 and a work memory 87 on the basis of a predetermined compression format. The compressed data is stored in an external memory 88 comprising a nonvolatile memory such as a flash memory or the like. According to the advance of the imaging apparatus development technique in recent years, a camera capable of selectively obtaining higher-resolution image data in addition to the normal photographing is available. Such high-resolution image data is compressed in the predetermined format in the same manner as above, and is stored in the external memory 88.
When the user observes already photographed image data, the compressed image data stored in the external memory 88 is expanded to normal photographed image data by the memory controller 85, and the expanded data is transferred to the video memory 89. In this way, the user can observe the photographed image via the monitor display 90.
As described above, in the digital still camera, when photographed image data is stored in a memory or the like, the image data is stored after it is compressed in a specific compression format or at a specific compression rate irrespective of its photographing conditions or photographing scene, or is compressed by a compression method or at a compression rate set by the user himself or herself.
However, in the digital still camera, since the photographed image data is uniformly saved by the camera irrespective of its contents, image data photographed in an optimal state (compression format) is not always saved. The same applies to a case wherein photographing for obtaining high-resolution image data is made, i.e., when the size of image data becomes large.
Even when the user himself or herself can set the saving method of the photographed image in advance, it is very cumbersome for the user to appropriately set the image compression method in correspondence with the intended photographed image. Hence, if the user has to set the saving method every time he or she takes photographs, he or she cannot immediately take photographs when the need for it arises, and misses a so-called shutter chance. Also, when an image photographing method must be set in addition to the saving method of the photographed image, such operations are harder except for expert users.
Along with advance of the digital technique in recent years, many imaging apparatuses capable of digital recording, i.e., so-called digital cameras have been proposed. Some of these digital cameras comprise a compact display device such as a finder or a TFT (Thin Film Transistor) liquid crystal display device for displaying an image to be photographed or a photographed image, a camera shake correction device for correcting a camera shake, and a large-capacity storage device such as a flash memory or the like for saving JPEG (Joint Photographic Experts Group)—compressed images.
The resolution of an image photographed by the above-mentioned digital camera is determined by the type of CCD used in the digital camera. Hence, in order to photograph a high-resolution image, a CCD having many light-receiving elements, e.g., million pixels or more, is required, resulting in an expensive digital camera.
On the other hand, a digital camera having a CCD with a small number of pixels improves the resolution by interpolation. Since the pixel value obtained by interpolation is the average value of surrounding pixel values, no problem is posed in a region with relatively flat gradation characteristics, but an image edge blurs in an image edge region where the gradation characteristics change largely.